1. Field of the Invention
The present invention relates to an image forming apparatus and an image correction method that perform an image correction operation, such as a color shift correction, for maintaining image forming quality.
2. Description of Related Art
Conventionally, an image forming apparatus that forms images using an electro photographic process such as a printer, a copier and a multifunction apparatus having printer and copier functions has been expected to reliably form high-quality images, amid recent trends toward full color, high quality pictures. To reliably form high-quality images, it is necessary to improve part precision and attachment precision of various components of an apparatus in the process of designing, manufacturing and adjusting of the apparatus. Those components include a laser scanning unit, a transfer belt and a photoconductor that are related to image formation. It is further necessary to consider effects over time, including a temperature change of components when using the apparatus. Therefore, there is a need to perform predetermined image correction operations, such as color shift correction, employed by a tandem system color image forming apparatus.
As a technology related to execution of such an image correction operation, an apparatus designed to maintain image quality without lowering image formation efficiency is available. For example, a color image forming apparatus is configured to form on a transfer belt a displacement detection pattern for detecting a displacement during a color image formation and to correct the pattern displacement based on detection results by a detector. Such color image forming apparatuses include a color image forming apparatus configured to extend, by a predetermined length, intervals for conveying sheets from a feeder to a transfer belt when the counted number of continuous printing exceeds a predetermined number, and to form a displacement modification pattern on the transfer belt at the extended intervals for conveying sheets (See Relate Art 1).
[Related Art 1] Japanese Patent Laid-open Publication 2001-290327
However, in the technology disclosed in Related Art 1, when the counted number of continuous printing exceeds a predetermined standard number (i.e., when image correction becomes necessary), intervals for conveying recording sheets from a feeder to a transfer belt are extended. Therefore, when the counted number of continuous printing exceeds the predetermined standard number while a print job for continuous printing is in progress, an interval between a start and an end of the print job becomes longer, thus resulting in a longer waiting time for users.
Further, when the counted number of continuous printing exceeds the predetermined standard number during duplex printing or printing using finishing features (sorting, stapling, punching, etc.), users may have to wait while a recording sheet remains in the apparatus after its one side has been printed, or while a printed sheet remains in a buffer tray for a finishing process. In that case, users may misunderstand that a jamming problem or an error has occurred, even though the apparatus is normally operating.